M931A2 Brakes

[captnron]

Can anyone send me some pics of the valves and plumbing that are located on the drivers side step. My brakes won't release. Changed all the check valves and spring brake pods. Wedges are greased and look great.

 

[tobyS]

What is your air pressure building to?

 

[98G]

I suspect the gladhand cover, service side on the front.

There's a vent on it. If it clogs or is removed, it prevents the service brakes from completely releasing.

 

[simp5782]

What is your spring brake tank air pressure? Not what the gauge is reading but the tank behind the drivers step. Rig up a gauge into the drain line.

 

[captnron]

My gauge reads 120, but I will rig a gauge to check that pressure tank.

 

[simp5782]

My gauge reads 120, but I will rig a gauge to check that pressure tank.

That tank behind the step is what controls the brake release. Not the tanks the gauges read off of.

If you have not replaced the check valve that feeds that tank then it probably will be the cause. I've seen it happen alot

 

[captnron]

I replaced both of those check valves, the tank has 110 pressure with a gauge connected to it.
when I step on my brake pedal air flows to my service brake chambers, and keeps flowing after I take my foot off the pedal?
Any thoughts?

 

[captnron]

What is your spring brake tank air pressure? Not what the gauge is reading but the tank behind the drivers step. Rig up a gauge into the drain line.

Can you pm me when you get a chance. Snowride800@hotmail.com

 

[simp5782]

Can you pm me when you get a chance. Snowride800@hotmail.com

should help you

 

[captnron]

should help you

My spring tank has air and pressure. 1st time you step on the brake pedal the brakes lock and won’t release. I took the line off the small pod and it has constant pressure. So it keeps my brakes on after the pedal is released

 

[simp5782]

My spring tank has air and pressure. 1st time you step on the brake pedal the brakes lock and won’t release. I took the line off the small pod and it has constant pressure. So it keeps my brakes on after the pedal is released

Bad treadle valve. Remove the third line down on the treadle valve then apply your brakes. It should send air out but stop when you are off the pedal

Top is primary supply. Second is secondary supply. 3rd is delivery. 4th is vent

 

[captnron]

Bad treadle valve. Remove the third line down on the treadle valve then apply your brakes. It should send air out but stop when you are off the pedal

Top is primary supply. Second is secondary supply. 3rd is delivery. 4th is vent

I will try that this weekend, let you know if that was it

 

[captnron]

I will try that this weekend, let you know if that was it

Well I replaced the treadle valve since I had one and still didn’t work. My service brakes have constant pressure. Could some air line be connected wrong?

 

[simp5782]

Remove the drivers side service sending line from the rear relay valve

There are two. One is above the rear rear axle and other one is above the front axle. It will be the only line coming into that relay from the drivers frame rail. It's a 5/8" wrench. Remove it and see if it has constant pressure.

They both T off at the Front relay so checking the rear one is fine and the easiest to get to.

 

[captnron]

Remove the drivers side service sending line from the rear relay valve

There are two. One is above the rear rear axle and other one is above the front axle. It will be the only line coming into that relay from the drivers frame rail. It's a 5/8" wrench. Remove it and see if it has constant pressure.

They both T off at the Front relay so checking the rear one is fine and the easiest to get to.

I removed the line off the aft ABS relay valve. There is not constant air. I pushed the brake pedal a few times see if the valve was sticking. There is no air when the pedal is not depressed

 

[simp5782]

I removed the line off the aft ABS relay valve. There is not constant air. I pushed the brake pedal a few times see if the valve was sticking. There is no air when the pedal is not depressed

No air on that service line with the pedal depressed?

But your service brakes are applied constantly? Or your spring brakes won't release?

 

[captnron]

No air on that service line with the pedal depressed?

But your service brakes are applied constantly? Or your spring brakes won't release?

Sorry for the confusion. No constant air to the relay valve. There is air when I Push the brake pedal. Can’t figure out why my service brakes will stay on when I let off the pedal.
When I remove the red air line from the double check valve on the driver side frame where the stop light pressure switch is mounted then my brakes work fine. That airline is connected to the outlet port of the double check valve

 

[simp5782]

Sorry for the confusion. No constant air to the relay valve. There is air when I Push the brake pedal. Can’t figure out why my service brakes will stay on when I let off the pedal.
When I remove the red air line from the double check valve on the driver side frame where the stop light pressure switch is mounted then my brakes work fine. That airline is connected to the outlet port of the double check valve

That same air line is going to the service port you removed from the relay. Check valve isn't letting the air exhaust with a closed circuit

 

[simp5782]

So you need to remove the check valve and complete the circuit to the rear relay valve. It the brakes work fine then ite that double check valve. If you have already replaced that valve let me know

 

[simp5782]

You have a few double check valves. # 6 is located drivers side frame rail right about where the transmission and engine bolt together.

Have you replaced it?

This is the first check valve that air goes thru from the brake pedal on its way to the rear brake relay.

You may also remove the vent line off of the treadle valve. It is the lowest line on the firewall. Just to check that something hasn't clogged that line